1. Field of the Invention
This invention relates to an ink-jet recording apparatus and a recording medium to be used with such an ink-jet recording apparatus. More particularly, the present invention relates to an ink-jet recording apparatus employing an electrostatic adsorption method for moving a recording medium.
2. Related Background Art
An ink-jet recording system adapted to eject fine ink droplets and causing them to adhere to a recording medium such as a sheet of paper for the purpose of recording images and/or characters provides a number of advantages including high speed and low noise operation, adaptability to multi-color recording, versatile recording patterns and non-use of both developing unit and fixing unit. It can be driven to eject fine ink droplets on any of a number of different operating principles. Because of the remarkable advantages, ink-jet recording systems have been used with increasing popularity in various applications including information devices for outputting/recording visual information. Additionally, images formed by a multi-color ink-jet recording system are comparable to those obtained by color printing using a plate or color photography in terms of image quality. Furthermore, the multi-color ink-jet recording system can produce images at low cost if compared with color gravure printing and photography particularly when the number of copies to be produced is small. Therefore, the ink-jet recording system is expanding its scope of application rapidly to cover full-color recording.
Of various known ink-jet recording systems, the recording system using a so-called full multi-head having a width comparable to the recording medium has been known to be advantageous for high speed recording. There has been proposed the use of an electrostatic adsorption belt for moving the recording medium for recording apparatus employing the ink-jet recording system. Ink droplets are ejected from the recording head onto the recording medium that is being adsorbed to the electrostatic adsorption belt and moved with the latter.
However, known electrostatic adsorption systems for moving a recording medium is accompanied by a number of problems. The recording medium has to be held flat while it is being moved and then quickly discharged from the electrostatic adsorption belt so as to be delivered to the outside of the system. However, ink mist can be produced and adhere to the surface of the recording medium when the ink is ejected from the recording head under the influence of the surface potential of the electrostatically adsorbed recording medium. Additionally, some of the ejected ink droplets can be deflected from the proper course also by the surface potential of the electrostatically adsorbed recording medium to consequently adversely affect the quality of the image formed on the recording medium.
The inventors of the present invention have been paying research efforts for dissolving the technological problems relating to the electrostatic adsorption system to which the physical, chemical and/or electrostatic properties of the recording medium may be responsible. To date, the properties of a recording medium have been studied and improved mostly from the viewpoint of the quality of the recorded image and the ink absorbability.
For instance, the recording medium is required to show enhanced properties in response to the improvements in the recording performance of the ink-jet recording system including high speed recording, high definition recording and full color recording. In an attempt at meeting the requirements for improving the properties, various forms of recording medium have been proposed to date. Some of them will be briefly examined below.
Japanese Patent Application Laid-Open No. 55-5830 proposes an ink-jet recording sheet comprising an ink absorbing coated layer on the surface of the support sheet thereof. Japanese Patent Application Laid-Open No. 55-51583 proposes an ink-jet recording sheet comprising a coated layer containing amorphous silica as pigment.
Any of the heretofore proposed ink-jet recording sheets is realized by forming an ink-receiving layer containing a pigment such as alumina or silica on a base sheet. Because of the arrangement of the ink-receiving layer, the proposed ink-jet recording sheets do not provide the handle of plain paper if they comprise a paper base member. Japanese Patent Application Laid-Open Nos. 6-312572, 7-25131 and 7-25132 propose a recording medium comprising a base paper that is slightly coated with ultra-fine pigment particles to a covering ratio of not less than 70% and having a recording surface that provides a surface profile of pulp fibers in order to give a touch of plain paper to the recording medium. Additionally, Japanese Patent Application Laid-Open No. 1-141783 proposes an ink-jet recording paper obtained by on-machine coating of amorphous silica and alumina hydrate and Japanese Patent Application Laid-Open No. 11-174718 proposes information recording paper coated with pigment size.
On the other hand, recording mediums prepared by internally adding one or more than one loading materials to paper have also been proposed. For instance, Japanese Patent Application Laid-Open No. 53-49113 proposes recording paper comprising a sheet containing internally added urea formalin resin powder and coated and impregnated with a water-soluble polymer. Japanese Patent Application Laid-open No. 58-8685 proposes recording paper comprising a sheet containing a synthetic silicate and glass fibers that are internally added and coated and impregnated with a water-soluble polymer. These inventions are intended to improve the ink absorbability of the recording medium by internally adding fine particles of one or more than one specific substances to unsized paper.
Recording paper having a multilayer structure is also proposed as a different form of paper containing one or more than one internally added substances. For example, Japanese Patent Application Laid-open No. 63-118287 and U.S. Pat. No. 4,734,336 propose uncoated paper prepared by bonding a support layer made of pulp fibers and a surface layer made of one or more than one loading materials such as silica and fibers. Japanese Patent Application Laid-open Nos. 1-78877, 2-243381, 2-243382 and 5-106197 propose multilayer recording paper whose layers are formed simultaneously and in which the base layer or the interface of the base layer and the surface layer is sized. Japanese Patent Application Laid-open No. 6-219043 proposes multilayer recording paper whose surface layer carries an inorganic substance that is hardly soluble or insoluble to water. Japanese Patent Application Laid-open Nos. 6-287886, and 8-258400 propose multilayer recording paper made by using a specific type of pulp such as bulky cellulose, mercerized pulp or bleached broad leaf sulfite pulp. Japanese Patent Application Laid-open No. 9-170190 proposes multilayer recording paper having a surface layer mainly made of hydrophilic or hydrophobic fibers and a base layer mainly made of cellulose fibers.
Thus, it has been realized that the recording medium is an important factor for improving the quality of recorded image and the speed of recording images and efforts have been paid almost exclusively to meet the requirements for improving the properties and hence the recording performance of recording medium. However, with any of the above listed techniques, it is difficult to realize a recording medium that meets the requirements for improving the recording performance and also dissolves the technological problems relating to the electrostatic adsorption system and an ink-jet recording apparatus adapted to use such a recording medium.
In view of the above identified problems, it is therefore the object of the present invention to provide an ink-jet recording apparatus adapted to adsorb and move the recording medium by means of an electrostatic adsorption system that can minimize the influence of the surface potential of the recording medium on the recorded image and at the same time meet the requirements relating to the recording performance and also a recording medium that can suitably be used with such an ink-jet recording apparatus.
According to the invention, the above object is achieved by providing an ink-jet recording apparatus adapted to eject ink from an ink-jet head onto a recording medium held in position by means of an electrostatic adsorption system, the surface resistance of the recording medium being not greater than 1xc3x971011 xcexa9/xe2x96xa1.
In another aspect of the present invention, there is provided a recording medium to be used for an ink-jet recording apparatus adapted to eject ink from an ink-jet head onto the recording medium held in position by means of an electrostatic adsorption system, the surface resistance of the recording medium being not greater than 1xc3x971011 xcexa9/xe2x96xa1.
Thus, as the surface resistance of a recording medium according to the invention is held to be not greater than 1xc3x971011 xcexa9/xe2x96xa1, the surface potential of the recording medium that is produced by electrostatic adsorption as a result of being moved by means of an electrostatic adsorption system is quickly reduced to 0V. Therefore, the problem of the electric field that is generated by the surface potential to deflect the ejected ink droplets and that of ink mist that can adhere to the recording medium can be effectively prevented from occurring.